Retaining Walls Archives

August 20, 2014October 19, 2017

One That Got Away: Challenging Retaining Wall in DC

One of my favorite things to do on this blog is to profile recent projects. It’s a fun opportunity to show what’s possible, and maybe brag a little. Hey, my clients let me create some great landscape designs for them!

As I was thinking about a recent sale I didn’t close I realized I should blog about it as well. After all, what killed the deal were the realities of the site and the budgetary challenges they created. There might be something to learn from this, especially if you’re planning a DC landscape design project of your own.

The site: A rowhouse in DC. It’s in a hilly neighborhood off of Rock Creek Parkway and there is a HUGE amount of elevation change between the street and the front porch.

All the homes in this neighborhood have a 10-12 foot tall stone retaining wall right at the city sidewalk. This client’s wall had deteriorated, so last year he had the wall rebuilt. Such a wall requires a huge cantilevered footing, which meant digging way back into the hill. Because the wall was being built right at the city sidewalk all excavated soil was hauled off site. The new wall was built, including a 4 foot wide set of curved steps, and only some of the removed soil was brought back.

The project for which I was called: Prior to the new wall’s construction, the homeowner had an 8-10 foot wide level piece of lawn in front of his porch. Since the wall builders didn’t bring all that soil back, it now plunged off like a ski slope. The homeowner, therefore, wanted one or two natural stone retaining walls built behind the big wall to level off the yard, new landscaping, and new low voltage landscape lighting.

Wowsers. The client wanted to have a sense of the budget, so my masonry contractor and I sat down, had some coffee, and talked it over.

The challenges:

– Access. Parking in DC is a challenge, and with the sheer wall right at the sidewalk there would be nowhere to stage materials. Everything would have to be hand carried up the steps and staged at the top of the lowest wall. If the steps were a straight shot, we could have laid boards as ramps and wheeled materials up – but that wouldn’t work on the curved steps. Getting concrete up to the wall footers would require a pump truck.

– Work area. The only space to stage materials and mix mortar is a small flat pad at the top of the new retaining wall. That means a lot of shuffling things around every day, reducing efficiency.

– Backfilling our new walls. Again, the material that was here originally never came back. This means that we would need to bring in between 40-60 cubic yards of fill dirt and topsoil. To put that in perspective, a full load in a standard tri-axle dump truck is 12-14 cubic yards.

So how would we get this quantity of soil up to the top of the site? As mentioned above, wheelbarrows were out. Hiring a ridiculous number of laborers and doing a bucket brigade would be just… ridiculous. We settled on having Sislers Stone put the soil in super sacks (sturdy bags that can hold a ton of bulk material), truck them to the site with a flatbed, and lift them into place with a rented crane. Logistics!

– Safety. Any time you have a retaining wall on a slope above another retaining wall, there’s a possibility that it will exert forces on the wall below. I let the client know that as part of the landscape design process I would have a structural engineer look at my drawings, and if he felt it required his involvement that would be an additional cost.

After all this, the landscaping and lighting were a small portion of the project cost, but it all added up. In the final analysis, we figured it would cost a minimum of $30,000 to complete the project. It was more than the homeowner wanted to spend, so we’ll hopefully revisit it later.

The unfortunate thing is that this is a $30,000 landscape installation project that could have been avoided, or at least reduced. The company that rebuilt the wall clearly didn’t work off of detailed plans or specifications. I know this because the client told me they built the steps in the wrong place, and there was clearly no communication up front about the soil hauled off site being brought back. This is yet another case where starting with a landscape designer – someone who could create a detailed set of drawings and a complete scope of work – could have saved thousands of dollars.

I would love to save you thousands of dollars! If you’re looking for a landscape designer for a project in northern Virginia, DC, or Maryland, contact us for a consultation!

February 20, 2013February 18, 2013

Building a timber wall – will it last?

I like to play a game I call underrated/overrated. You can play it with bands, actors, foods, anything you want. Example: underrated/overrated = Hudson Hawk is a brilliant and underrated movie/ Sideways is an incredibly overrated movie that makes me want to guzzle Merlot out of spite. See how it’s done? Please leave your own under/over thoughts in the comments.

A part of the landscape that I think is underrated is the timber retaining wall. There are two objections that I see raised about them: aesthetically they aren’t great, and wood will eventually break down and the wall will fail. Both very valid points. However.

Pressure-treated timbers are typically what you use for a timber retaining wall. The fun fact about pressure treated wood is that it is warrantied – but putting it in continuous contact with the ground voids the warranty. Even so, you can reasonably expect to get anywhere from 10-20 years out of a timber wall. We did a job a couple of years ago where we removed a timber retaining wall so we could install a new Techo-Bloc wall. The existing wood wall was fifteen years old and we expected it to come apart like a castle made of wet Kleenex. Instead it took days of work with demo saws and pry bars. Fifteen years later and the wall was still solid. I was impressed.

How do you get a wood wall to last so long? It all comes down to proper installation. I refer everyone to the Fairfax County Retaining Wall Detail packet, because it applies to most cases. You want a solid, compacted gravel footer; you want to make sure that every timber is level and true as it’s installed; you want to use 1/2″ galvanized spikes to hold the wall together; you want to use deadmen as shown to tie the wall into the grade behind it; and you want to backfill appropriately, including clean drainage stone, to keep water from causing the wall to fail. It may not be easy to execute (it’s still a lot of work and it takes skill to do well) but the principles are sound.

“But Dave,” you may say, “that doesn’t address the fact that a timber wall looks like a stack of lumber in my backyard.” Well, fair point my imaginary naysayer. This is why I don’t recommend a timber wall in every situation. If the wall is going to be front and center as someone drives into your property, it’s probably not the ideal choice. If you just need a functional wall and you won’t often see it, though, a timber wall could be a great way to make room in the budget for something else. In this scenario, we had to build the grade up almost six feet to create a waterfall. Rather than spend thousands of dollars to retain the soil at the back of the falls with a gorgeous stone wall that only the deer and squirrels would see, we used a timber wall.

Worried about the aesthetics? This is what it looks like from the house. Yep, you don’t see it.

There you have it: the humble timber retaining wall. It may not be glamorous and it may not be a forever solution, but if you need to stretch the budget and can conceal the wall, I hope you’ll at least consider it.

Are you making a major change to your landscape and looking for ways to stretch your budget and still make it look great? I can help with that! Contact me to set up a consultation. I’d love to help you fall in love with your property all over again.

August 22, 2011

How Much Does a Retaining Wall Cost in Northern Virginia?

I recently spoke with someone who was looking for a retaining wall, four feet tall and ninety feet long. Before moving forward with a consultation he wanted a sense of what such a wall would cost.

He was surprised, to say the least.

There are a lot of design consideration for retaining walls in northern Virginia, and every site is different. Slope, soils, access, permits, and existing conditions impact the costs, so it’s not generally practical to create a proposal for a retaining wall based solely on square foot pricing. The best contractors examine the site, create a landscape plan (or have a landscape designer create a plan), work out all the materials needed down to the number of tubes of adhesive, and base the price on the labor and materials required to build that individual wall.

That said, I will use square foot numbers to at least start the conversation so I can help the client decide if they’re ready to move forward with the design. When we multiply the length of the wall by the height we get the total square feet of face, or SFF. Here’s how different materials can break down by SFF. Keep in mind that these are not absolutes, just starting points. Your site conditions may result in higher or lower costs.

Pressure-treated 6×6 retaining wall: Generally, a wall of this type will start at $35-45/ SFF. So in the example conversation with the homeowner who had a 90’x4′ wall (360 SFF), he’s looking at approximately $12-16K.

Segmental retaining wall: these are your interlocking concrete wall systems, EP Henry, Techo-Bloc, or similar. Depending on a lot of variables, walls average from $50/SFF to $75/SFF. For our homeowner with 360 SFF of wall, we’re looking at approximately $18-27K.

Concrete retaining wall with stone veneer and cap: This is the most attractive type of wall, and one I’m a huge fan of. Costs vary by site conditions, stone used, etc., but I generally ballpark $75-105/SFF when discussing budgets. My sample homeowner with 360 SFF would be looking at a range of $27-38K.

There are other types of walls (boulder, dry-stacked fieldstone, poured and stamped concrete, etc) but the above are far and away the most commonly requested and built in the DC Metro area. As you can see, retaining walls have the potential to use a good portion of the budget for a landscape project. This is why good design is key. Not only can a good landscape master plan ensure that the walls are where they need to be and and properly designed, it can potentially reveal options for using fewer or smaller walls – freeing up funds for the more exciting parts of the project.